Shaquille O'Neal Says He'll 'Will Smith' Charles Barkley In Hilarious Freestyle

Charles Barkley better keep his head on a swivel -- Shaquille O'Neal says he'll follow Will Smith's lead and slap the hell outta his TNT co-host ... dropping the playful threat in a hilarious freestyle rap.

The Big Aristotle made the comment at his surprise belated birthday party at Steak Market in Atlanta on Wednesday ... when the crowd of about 250 people asked him to get up to the DJ booth and give them a set.

The NBA legend ended up grabbing the mic and spitting off the dome for about 10 minutes instead ... name-dropping his "Inside the NBA" friends and referencing the infamous Oscars moment in the process.

"Tomorrow I'm on TNT, with f***ing Kenny, with f***ing Chuck, I might Will Smith his ass I don't give a f***," Shaq raps.

Unlike the real interaction, everyone loved the reference ... cheering and laughing after Shaq dropped the line.

Now, Shaq and Chuck have had a playful rivalry for years ... with both Hall of Famers going back and forth at every possible opportunity.

O'Neal was letting the insults fly on more than just Barkley, though -- he even brought up LeBron James while dissing a dude's hairline ... which was a crowd favorite as well.

The whole bash looked fun as hell -- it was sponsored by D'usse, so you know the adult beverages were flowing.

Celebs like Bobby Valentino and 2 Chainz were also in attendance ... as well as a tiger.

As for Shaq's birthday, it was March 6 ... but hey, better late than never!!